One Business System Per Client

Going in, I figured I could have multiple business systems tied to a single technical system. For example, if I have a techical system (SAP R/3) of RD0 110, and I want to have one business system for a vendor price check, another for sending ship notice idocs to a 3rd party server, etc.

When I go to add a second Business System to RD0 110 in SLD, I get an error that "The selected client already has a business system. Select a different client or system.".

Where am I going wrong?